Electric organ system



June 29, 1943.

HARHOMIC GE'IVEPA TOR C A. R. RIENSTRA ELECTRIC ORGAN SYSTEM Filed May 31, 1941 AMI? HARNON/C F IL TERS CON TROL AND MIXER UNIT BY 1 fiA-Mw.

6 LOUDSPEAKER AMP. 7

A. R. R/ENSTRA A 7' TORNE Y Patented June 29, 1943 UNITED STATES; PATENT I 2.22am

orrica ELECTRIC ORGAN SYSTEM Albert R. Bienstra, Garden City. N. Y., alolgnor to Bell Telephone Laboratories, Inc New York, N. Y., a corporation of New York Application May 31, m1. Serial No. muss Claims. (01. 84-l.23)

This invention relates to electric musical instruments and more particularly to an electric organ system in which the tones are produced by electric generators. 1

m the electric organs of the prior art there have been supplied at least twelve oscillators or alternating current generators for producing the tempered basis.

This invention attains the foregoing object by providing less than twelvegenerators, each adapted to provide an output rich in harmonics, the fundamental frequencies of these generators being tuned to particular frequencies in. an octave below the lowest octave of the instrument, and a filter means; for each generator adapted to segregate into separate channels, the several harmonics produced by each generator.

Th invention may .be better .understood by referring to the drawing in which:

Fig. 1 represents schematically the tone generating system of this invention; and

Fig. 2 discloses a preferred form of filter means.

Referring now to Fig. 1., a plurality of primary generators I, less than twelve in number, are provided to .generate frequencies in the octave next below the lowest octave of the keyboard. In the particular embodiment disclosed, five such generators are used and are indicated as har-' shown, for example, by United States Patent 2,023,436, issued December 10, 1935 to D. Prinz, by 2,117,752, issued May 17, 1938 to L R. Wrathall, and by 2,181,280, issued'November 28, 1939 to i R. L. Miller.

The fundamental frequency of harmonic generator C corresponds to an octave below the lowest 0 on the keyboard, for example, 18.333 cycles per second. This, as hereinafter more fully shown, will provide A4 withthe standard free quency of 440 cycles per second. Obviously the tuning may be standardized on a pitch other than the one here chosen for illustrative purposes. The fundamental frequencies of all five primary generators are chromatically related on an equally tempered basis as'shown in Table I.

' Tun: I

' Fundamental Primarygenentor I c- 1am Cl l7. 1) mm m 10.04 a 2am 2mm r: zuzs In the foregoing table it should be remembered that the fundamental frequencies listed are those which correspond with the fundamental frequencies of the oscillators in the generator octave, that is the octave next ,below the lowest octave appearing on the organ keyboard. The purpose of primary generators F and F# will be described later.

As previously stated the output of each of these generators is rich in harmonics. These harmonies are segregated into separate channels by means of a'filter system 4 from which it is fed into a control and mixer unit] where the various segregated harmonic components are synthetically combined in a well-known manner and fed to an output amplifier 6 and loud-speaker system 1. Any of the well-known control and mixer systems may be used suchas, for example, those shown in United States Patents 1,953,753 to Firestone, issued April 3, 1934, 2,103,169 to Midgley, issued December 21, v1937 or 2,139,023

to Kock, issued December 6, 1938.

Each unit of the filter system comprises a plurality of mechanically vibrant reeds M which are electromagn'etically driven fromdriving coil I connected to the output of one of the generators. Each of these reeds is resonant to some harmonic produced by its associated generator. In th specific embodiment herein disclosed an electrostatic pick-up means is shown which comprises an electrostatic pick-up plate ll cooperating with the reed l0 so that as the reed vibrates it produces a. varying capacitance. All of the reeds in the entire organ are electrically connected'together and to the control and mixer uni-t via common conductor l3. Each electrostatic pick-up plate ii is connected to the control and mixer unit 5 by way of its associated -denotedCandGinthe conductor If. A condenser I may be connected across each of the filter driving coils in order to resonate certain frequency regions to obtain desired tone qualities according to the formant theory. In this case certain frequencies are emphasized or suppressed for all notes of the keyboard, regardless of the pitch of the fundamental. The advantage of doing this here rather than in the control unit is its simplicity and cheapness as only one electrical filter is required for each generator. m combination of coil and reeds forms an electromechanical filter.

Random phase relationships are thought desirable and this invention achieves this end by using reeds which inherently have no fixed phase relationships between the several harmonics of a tone.

Generators C#. D and D# have been omitted from the drawings for the sake of clarity. However, they are connected as shown for generators C and E and have the frequencies assigned to themasshownin'lablelabove.

Although only five generators are used. all twelve notes of each octave are produced on a substantially correct equal tempered basis. The generators which are used for producing the variOus notes are shown in tabular form in Table II below:

Asshownin'rablenaboveallofthenotes tireorganofseven of the C generator. In addition mentalfrequenciesofnotes CandGforallthe octaves of the organ. nineteen additional harmonies, making twenty harmonics in all, including the fimdamental, are also produced. Of course. some of the upper harmonics for the hlsher notes C and G become inaudible and for that reason they are not supplied. However, all twenty harmonics for each note are supplied wherever theyare within the audible range. To dothisaiifilterreedsarerequiredasshownin the table.

organ are produced by a process of frequency division.

The manner in which the fundamental frequencies for the first octave of the organ are derived from the five generators is shown in tabu- The first column of Table III lists the twelve notes of the first octave. The sewnd column shows that the fundamentals of the first five notes are derived from the second harmonics of the five primary generators, the fundamentals of the last five notes are derived from the third harmonics of the same generators and the remaining two notes F1 and F1# are derived from primary generators D# and E, respectively by extracting the fourth subharmonics of their ninth harmonics. The third column list the actual frequencies derived and produced by the organ and the last column lists for purposes of comparison the correct equally tempered frequencies based on Ac=440 cycles per second. It will be noted that the system of this invention provides a substantially correct scale of equal temperament and the error are of no practical importsimilarly. the fundamental frequencies for all oftheC#andG#notesaswellastheharmcnics thereofareproduoedfromgeneratorc#andaa reedsarerequired. AlsoallthenotesdenominatedDandAareproducedfromgeneratorD and 91 reeds are required. Generator D# producesallofthenotesD#.A#andl 'requiring 107 reedsandgeneratorltproducesallofthe notesdenotedE,Bandl"#,thisrequiringl06 reeds; Inthelasttwocasesallofthenoteslbit and A#, E and B are produced as for the first three generators, but thenotes 1' and I"# arenot allproducedinexactlythesameway. Someof theharmonicsofl'andr#intbefirsttwo octaves as well as all of, their harmonics, including the fundamentals. for the remaining octaves are produced as previously described. However. the fundamental and some of the harmonance. It mayalsobenotedthatthescalecontains a number of perfect musical fifths. For example the major chord on C1 is built on an equally tempered major third and a slightly sharpened equally tempered minor third, thereby causing the interval from the tonic to the dominant to bee perfect fifth and the tonic to the mediant to be an equally tempered major third. While the chord is still not perfect, it is slightl! improved by the departure from strict equal temperament.

In the second octave the notes F: and 1m: are obtained by extracting the second subharmonics of the ninth harmonics of the D# and E primary generators, respectively. All of the fundamental frequencies of the notes in the remaining octaves are obtained by selecting the appropriate harmonies of the five primary generators. of the 107 filter reeds required for the D# primary generator, 88 of them are utilized for producing all of the D# and A# notes of the keyboard together with all their audible harmonics up to and icsofl 'andl 'itinthefirsttwooctavesofthey including the twentieth harmonic. In addition these same reeds produce all the fundamental frequencies for the F notes of the keyboard together with many of their harmonics with the exception of notes F1 and F2 in the first two octaves as previously stated. The remaining nineteen reeds are used to produce the harmonics of the 1'' notes not produced by the 88 reeds.

The necessary subharmonics are provided by two groups of multivibrators I4 and II shown in block form in Fig. 1. Group II produces the aces 242 fundamental frequencies for notes Pi and l": and

produced by the D# primary generator. Group II does the same for notes IMF and PM. The mannor in which this frequency division is accomplishedistabulatedinTableIVbelow: F t a L T w I or seven genera or For five generat rs Number reeds required Harmonic x u g l 9 a i It will be noted that the number of reeds for g g: the first three generators are the same as given a -II III is 4% in Table II. However, the number given for genm g erator D# and generator E are here given as 88 which is the actual number required to segregate notes D#, A# and E, B, respectively,toget her 3 with their several harmonics. Only fifty-four filter reeds are used with generator F because it 153/; provides only the note F and its audibl harg monies. For the same reason onl fifty-three.

o0 filter reeds are used with the F# generator. The

actual frequencies derived from the seven 1:11--

The above table is specifically for notes F1 and F: but notes F1# and F2# use the same division scheme except they derive their frequencies from primary generator E instead of D# as was also .indlcated by Tables II and III. Inspection of Table IV discloses that each of the multivibrator groups It and it contain ten units capable of providing the fourth and second subharmonics of the ninth, twenty-seventh, forty-fifth, sixty-third, eighty-first, ninety-ninth, one hundred seventeenth, one hundred thirty-fifth, one hundred fifty-third and one hundred seventy-first harmonies of their primary generator. All these harmonics appear among the filter reeds of their associated primary generators so that no additional reeds are needed.

The foregoing description has set forth in considerable detail the manner in which the various fundamental frequencies of a seven octave keyboard together with twenty audible harmonics thereof are produced by five primary generators, two groups of frequency dividers and a set of filter reeds. By way of restatement the invention thus far described may be summarized as follows:

1. All of the fundamental frequencies together with a wide range of their harmonics for an entire keyboard with the'exception of notes F1, F2, PM and F2# in the first two octaves are produced directly by five primary harmonic generators.

2. The frequencies thus produced are segregated for purposes of controlled synthesis by means of five groups of electromechanical filters of the reed type.

3. Notes F1, F2, F1# and F2# and most of their harmonics are obtained by multlvibrators excited from the output ofcertain of the filter reeds driven by the D# and E generators; their remaining harmonics'are derived directly from filter reeds driven by the D# and E generators.

The use of multivibrators is obviated by using seven primary harmonic generators instead of only five. In addition to the five primary generatcrs already described, the generator octave also 78 contains primary generators l" and l"# with the fundamental frequencies shown in Table I above.

The number of filter reeds for each of the seven primary generators is given in Table V below.

mary generators as well as the manner in which they are derived is shown in Table VI.

Tana: VI

For seven generators A t l Corrlalct 0 us equn y- Notes Derived frequency tempered frequency 32. 67 32. 70 34. (ll 34. 65 36. 67 36. 71 38. 85 38. 41.16 41. Z) 43. 65 43. 65 46. 25 46. 25 49. (I) 49. 00 51. 91 51.91 55. (I) 55. (I) 58. 27 58. 27 61. 73 61. 73

It will b noted that all the frequencies are the same as given in Table II except for the frequencies of F1 and F1# which are arbitrarily made equal to the frequencies for these notes as they appear in the correct scale of equal temperament. These two notes could have followed strictly the scale of equal temperament built up from C=16.333 in which case F1 and F1# would have been 43.60 and46.20 cycles/second, respectively. The differences being small, either set of values may b regarded as following substantial equal temperament.

A preferred means of driving the harmonic filters or reeds of Fig. 1 is shown more particularly in Fig. 2. In-this figure, a plurality of harmonic reeds I0 are mounted by means of a suitable support It to a diaphragm l1. Diaphragm-ll is driven by coil 8 shown in Fig. 1 from the output of its associated primary generator in a manner well known to the art. Some shielding is required between the filter reeds. However, inasmuch as the principle of shielding is so well known in the art, no shielding is shown in this figure for the sake of clarity. One of'the pick-up plates l I is shown associated with one of the filter reeds ll. The remaining pick-up plates have been deleted. Conductor l2 connects pickup plate II to the control and mixer unit I as shown in Fig. 1. Conductor II which is connected to the diaphragm support II is the commonconductor It also shown in Fig. 1 wherein is shown all of these diaphragm supp rts electrically connected together. All of the filter reeds ll of each of these filter units are electrically connected to their diaphragms ll through their supports l6 and consequently to their diaphragm supports it so that effectively they are all connected to their common conductor ll.

Each of the harmonic generators of Fig. 1 have connected to the output circuits thereof several of these harmonic filter units with their coils I serially connected as indicated in Fig. 1. The actual number of units which it is necessary to connect in series is determined only by the number of reeds which the particular design will permit to be mounted on any one harmonic filter unit.

Whil the invention has been described and illustrated by the disclosure of specific instrumentalities it should not be construed as limitedthereto but may include all reasonable equivalents within the scope of the appended claims.

Whatisclaimedis:

1. An electric organ system having a convenflonal twelve-note octave comprising the combination of five harmonic generators, the fundamental frequencies whereof are tuned in equal temperament to the first five chromatic tones of an octave below the lowest octave on the keyboard, a filter system comprising a series of hermonically related mechanically vibrant elements for each generator responsive to the output thereof for segregating into' separate channels the several harmonics produced by each generator, and a frequency divider system responsive to the output of some of the channels to provide two of the twelve notes in the first two octaves and some of the harmonics thereof, whereby all of the fundamentals and audible harmonics for the entire instrument are provided on a substantially correct equally tempered basis.

2. An electric organ system having a conventional twelve-note octave comprising the combination of five harmonic generators, the fundamental frequencies whereof are tuned in equal temperament to the first five chromatic tones of the octave next below the lowest octave on the keyboard, a filter system comprising a series of harmonically related mechanically vibrant elements for each generator responsive to the output thereof for segregating into separate channels the several harmonics produced by each generator. and a frequency divider system responsive to the output of some of the channels to provide two of the twelve notes in the first two octaves and some of the harmonics thereof, whereby all of the fundamentals and audible harmonics for the entire instrument are provided on a substantially correct equally tempered basis.

3. An electric organ system having a conventional twelve-note octave comprising the combination of five harmonic generators, the fundamental frequencies whereof are tuned in equal temperament to the first five chromatic tones of an octave below the lowest octave on the keyboard, a filter system comprising a series of harmonically related mechanically vibrant elements for each generator responsive to the output thereof for segregating into separate channels the several harmonics produced by each generator, and a frequency divider system responsive to the output of some of the channels to provide some of the notes for at least one of the octaves of the keyboard and some of the harmonics thereof, whereby all of the fundamentals and audible harmonics for the entire instrument are provided on a substantially correct equally-tempered basis.

4. An electric organ system having a conventional twelve-note octave comprising the combination of seven harmonic generators, the fundamental frequencies whereof are tuned in substantial equal temperament to the first seven chromatic tones of an octave below the lowest octave on the keyboard, and a filter system comprising a series of harmonically related mechanically vibrant elements for each generator responsive to the output thereof for segregating into separate channels the several harmonics produced by each generator, whereby all of the fundamentals and audible harmonics for the entire instrument are provided on a substantially correct equally tempered basis.

5. An electric organ system having a conventional twelve-note octave comprising the combination of seven harmonic generators, the fundamental frequencies whereof are tuned in substantial equal temperament to the first seven chromatic tones of the octave next below the lowest octave on the keyboard, and a filter system comprising a series of harmonically related mechanically vibrant elements for each generator responsive to the output thereof for segregating into separate channels the several harmonies produced by each generator, whereby all of the fundamentals and audible harmonics for the entire instrument are provided on a substantially correct equally tempered basis.

-ALBERT R. RIENSTRA. 

